Diabetic retinopathy (DR) and retinopathy of prematurity (ROP) are characterized by vessel loss followed by hyper-vascularization at the non-vascularized border. These vessels fail to grow into and rescue hypoxic retina and are misdirected towards the vitreous with formation of contractile bands and retinal detachment. If hypoxic retina could revascularize properly, destructive neovascularization (NV) would not occur. The misdirected NV is thought to result from high levels of pro-angiogenic factors released from hypoxic retina into the vitreous. Yet levels are even higher in hypoxic retina. We hypothesize that vaso-repulsive factors from stressed neurons prevent revascularization. Neuronal guidance cues, Semaphorins (Sema) and their receptor Neuropilin (Nrp) might be shared with vessels to direct this misguided growth. Nrp-1 binds opposing factors Sema3A and VEGF. Sema3A provokes EC apoptosis, inhibits VEGF dependant chemotaxis and could mediate cross talk between vessels and neurons. Hypothesis: Stressed ganglion cells (RGC) produce Sema3A which promotes vessel loss via EC apoptosis and repels growing neovessels from hypoxic retina towards vitreous. Suppressing Sema3A promotes revascularization and prevents retinopathy. Preliminarily we find that Sema3A is induced in stressed RGCs by hyperglycemia as well as in oxygen- induced retinopathy (OIR). Sema3A is elevated >25X in vitreous with proliferative DR. Blocking Sema3A in RGCs in OIR suppresses vascular loss (VO), improves revascularization of hypoxic retina and decreases pathological NV, suggesting a fundamentally new approach to treat retinopathy. We will test this hypothesis in diabetes models, in OIR, in vitro (RGCs and ECs) and ex vivo with aortic explants with O2 and glucose stress simulating phases I, II of retinopathy. We will: AIM 1 temporally quantify and localize retinal Sema3A, Nrp1, VEGF in DR, OIR. AIM 2 in DR, OIR determine if Sema3A suppression in retina or in RGCs suppresses retinopathy in mice with mutant Nrp-1 binding VEGF but not Sema3A and in WT mice with lentivirus (Lv)-driven shRNA targeting Sema3A in RGCs. AIM 3 in vitro determine competition between Sema3A and VEGF on vessel guidance and EC apoptosis and determine molecular signaling mechanisms. The proposed studies are pioneering as they would establish neuronal influence on vaso-degeneration and the importance of vascular repulsive cues in retinopathy. Our results suggest that the Sema3A-Nrp axis is likely to be an attractive therapeutic target to promote revascularization in retinopathy and other pathologies such as cancer and cerebral- vascular infarcts where vascular re-growth is a key determinant of area of injury.